Magnetic alloy material and device utilizing same

ABSTRACT

Magnetic devices depending for their operation upon remanent magnetization include alloys containing from 75-95 weight percent cobalt, 0.5-17 weight percent gold, remainder iron, such alloys being cold drawn so as to result in a minimum thickness reduction of 20 percent.

United States Patent [72] Inventors Gilbert Y. Chin New Providence; Donald Jafie, Emmaus, Pa.; Ethan A. Nesbitt, Berkeley Heights [2]] Appl. No. 871,130

[22] Filed Oct. 6, 1969 [45] Patented June I, 1971 [7 3] Assignee Bell Telephone Laboratories, Incorporated Murray Hill and Berkeley Heights,

Original application Sept. 5, 1967, Ser. No. 665,340, now Patent No. 3,511,639. Divided and this application Oct. 6, 1969, Ser. No. 871,130

[54] MAGNETIC ALLOY MATERIAL AND DEVICE UTILIZING SAME 5 Claims, 3 Drawing Figs.

[52] US. Cl 340/174 [51] Int.Cl Gllc 11/12 340/174;

[50] Field of Search I 75/170; 148/3l.55,3l.57

[ 56] References Cited UNITED STATES PATENTS 3,067,029 12/1962 Gyorgyetal. 75/170 3,098,803 7/1963 Godyckietal... 340/174x 3,350,180 10 1967 Croll 340 174x 3,355,724 11/1967 BlOWnellelaL. 340 174 3,390,443 7 1968 Gouldetal. 340/174x 3,407,397 10/1968 Snare 340/174 3,422,407 1 1969 GOUIdelai... 340/174 3,435,436 3/1969 Conrath 340 174 OTHER REFERENCES IBM Technical Disclosure Bulletin, Magnetic Thin-Film Alloy With Improved Thermal Stability by Ahn et al.; 10/8; No. 10; 3/66, P. 1419, copy in 340- 174 materials Primary ExaminerStanley M. Urynowicz, Jr. Attorneys-R. J. Guenther and Edwin B. Cave ABSTRACT: Magnetic devices depending for their operation upon remanent magnetization include alloys containing from 75-95 weight percent cobalt, 0.5-17 weight percent gold, remainder iron, such alloys being cold drawn so as to result in a minimum thickness reduction of 20 percent.

l6 l9 l7 l8 READ XPVXJESTEE READOUT PYYEE PULSE SOURCE SOURCE SOURCE 111 f u r 1 2 J PATENTEU JUN 1 I97! SHEET 2 [1F 2 FIG? STRESS, 0' (Kpsi) 7 0 6| C 2 l 8 h 5 2 I u l A 6 3' I 2... 1 l 0 0 O O O O 0 O 5 4 3 2 l women M33500 2 moz Iu .Pzmumw STRESS, o" (K /mm READ PULSE SOURCE "Y"WRITE PULSE SOURCE READOUT CIRCUIT "x"w RITE PULSE SOURCE MAGNETIC ALLOY MATERKAL AND DEVICE UTILIZING SAME This is a division of application Ser. No. 665,340, filed Sept. 5, 1967 now U.S. Pat. No. 3,511,639. This invention relates to alloy materials.

The materials of this invention are considered to be of particular interest in the fabrication of magnetic elements depending for their operation on remanent magnetization. This is a broad field of interest which encompasses magnetic switches and memory elements generally.

The design and fabrication of remanent magnetic elements is a sophisticated science having resulted in a large number of devices showing varying characteristics fulfilling varying needs. Such devices include the now common core memories which may take the form of a pierced sheet of US. Pat. No. 2,912,677 issued Nov. 10, 1959 to R. L. Ashenhurst et al., the twistor of US. Pat. No. 3,083,353, issued Mar. 26, 1963 to A. H. Bobeck, the laddie of US. Pat. No. 2,963,591, issued Dec. 6, 1960 to T. H. Crowley et al., as well as the various devices described in U.S. Pat. No. 2,736,880, issued May 11, 1956 to J. W. Forrester.

Most of these devices depend for their operation on the presence of remanence, that is, the ability of the material of which the memory element is constructed to remain magnetized after removal of an applied field. lnterrogation of such an element involves reversing the direction of magnetization, often by the field produced by one or more associated current paths. Many element arrays utilize coincident current paths and so require the passage of half currents" (each equal to one-half the current volume required to produce a field necessary to overcome the coercivity of the material) in both paths simultaneously. Reading is accomplished by sensing the current induced in an associated winding by flux reversal with such current or currents.

Most magnetic memories and magnetic switches now in use are temporary in that the flux switching which occurs during the readout cycle for any segment magnetized during the write cycle leaves the element in its initial magnetic condition, that is, the condition representing no information storage. Such destructive memories are useful in many switching and memory applications. For example, in most parts of a computer, there is no need to store the problem after the circuit has yielded the answer. Similarly, in may switching applications, it is necessary only for the switching to perform its function once with no requirement of permanent storage.

There are, however, numerous situations calling for apparatus designs in which information once stored must be yielded repeatedly. This is true in many uses of the twistor in electronic switching where the storage elements serve to define a particular circuit path which is necessarily the flexible response to a given interrogation. At this time, this desideratum is often served by associating a plurality of small permanent magnets with the bit locations intended to yield induced current upon interrogation, the remanent magnetization of the permanent magnets being sufficient to overcome the coercivity of the softer magnetic material of which the element is constructed. in other circuitry, this may be accomplished by the use of a constant DC bias through a current path. An example of the latter is the biased core access switch often associated with memory arrays.

More recently, effort has been directed toward the development of an electrically alterable permanent memory element operating on the piggyback principle. An example of this type of element is described in US. Pat. No. 3,067,408, issued to W. A. Barrett, Jr. on Dec. 4, 1962. Such devices depend for their operation upon the cooperation between magnetic materials of different remanence and coercivity in a manner such that the material with the larger value of remanence and coercivity (the harder material) influences the magnetization of the material of lower value of remanence and coercivity (the softer material) in a desired manner. in the operation of such a device, an information bit is stored at an address along the hard material by magnetizing the address bit in a direction as a representative of a binary l or form. This is typically accomplished by the use of coincidentcurrents. The more easily switched soft material, which is magnetically coupled to the hard material experiences a slave magnetization of opposite direction.

Readout of the stored information is accomplished by applying a magnetomotive force sufficient to switch the magnetization of the slave element but insufficient to effect the magnetization of the higher coercivity material. The readout magnetomotive force is such as to reverse the magnetization direction of all those slave bits that are coupled to the readout drive line. The electromotive force induced by those slave bits that change magnetization direction, say from 0, is the readout which describes the information stored in the high coercivity element. Once the readout operation is terminated by cessation of the applied readout force, the slave element will immediately be influenced by the magnetization of the stored information bit and its original direction of magnetization will be restored.

In order to perform in the manner described, the magnetic materials employed must have several specific properties. The hard memory bit in which the information is stored must have a high coercivity in comparison tothe slave material in order for it not to be affected by the magnetomotive force used to switch magnetization in the slave direction readout. lts

remanence must be high so that once readout is terminated, there will be a magnetic field of sufficient value to influence the direction of magnetization in the slave material.

In addition, the permanent storage material of the slave material should exhibit square DC hysteresis loops; that is, the ratio of the remanent magnetic induction to the saturation magnetic induction should approach unity. Square loopcharacteristics are important in order to approach a truly binary operation, where ideally the magnetic induction of a magnetic material switches between its positive and negative saturation values at a precise magnetic field intensity. Similarly, squareness obviates the need for currents to maintain the information throughout the storage life of the information bit since substantial diminution in the saturation magnetization will not occur.

The instant invention derives from the discovery that alloy materials within a defined compositional range, when processedin accordance with a specific schedule of conditions evidence a level of magnetostriction significantly lower than that evidenced by prior art materials commonly utilized in such applications. These materials have been found to evidence a square hysteresis loop with a high value of residual induction, a coercive force that can be varied up to 35 oersteds, (the range of 10 to 20 oersteds being of interest for twistor applications) sufficient ductility to permit processing to a fine wire and tape, and a minimum change in magnetic properties with'stress. The materials of this invention are alloys of the composition, 75-95 weight percent cobalt, 0.5- -l7 weight percent gold, remainder iron, to which standard additions may be made and in which certain unintentional inclusions may be tolerated. Above 95 percent cobalt, an undesirable hexagonal phase appears. Below 75 percent, the lower level of magnetostriction is lost with the concurrent formation of a body centered cubic lattice region. A preferred range of inclusion of this ingredient is from -85 weight percent, based upon the same considerations. Gold inclusion of at least the minumum indicated is required in order to retain control overthe coercive force of the composition. A gold content of more than 17 percent poses a problem since it is difficult to get such quantities into solution. A preferred gold range is from 3-9 percent. An optimum composition has been found to be one containing 82 percent, by weight, cobalt, 6 percent, by weight, gold, remainder iron.

Other inclusions, intentional and unintentional, are known to those skilled in the art and are included or tolerated to certain limits for reasons which are understood. Thus, manganese may be present in an amount up to about 1 percent, by weight,

based on the total composition, this inclusion is designed to.-

bind any sulfur commonly present in commercial materials.

Suitable alternatives are beryllium, magnesium, calcium, and so forth. Aluminum, frequently added to control oxygen, may be added in an amount of up to one-fourth of 1 percent, by weight. Frequently encountered unintentional ingredients include nickel, often at a level of one-half of 1 percent, in certain commercial materials, tolerable up to a level of about 2 percent. Silicon may be present in an amount of about 2 percent, upon which workability is impaired. Similar considerations apply to molybdenum and tungsten, also tolerable up to about 2 percent, phosphorous and sulfur, only tolerable up to about 0.1 of 1 percent, and manganese to about 2 percent.

Necessary processing constitutes the final steps of cold working such as to result in a minimum thickness reduction of 20 percent, as calculated from the fraction r,z,/t, where t, and t, are a dimension subject to reduction during working, before and after reduction. A heat treatment step may be desired for the purpose of generating specific properties or to satisfy device requirements and is carried out over the temperature range of from 100 to 1,000 C. for the minumum time required to bring the body undergoing processing to such temperature for a period of at least 1 second. Typical heat treatment schedules are from 1 hour to 16 hours over the indicated temperature range, where a total thickness of onehalf inch or greater is to be treated, and from one second to 60 seconds, where a single strand of material of thickness up to 0.025 inch is treated separately. Cold working may take any of the usual forms so long as the reduction as specified is accomplished. Forms of reduction found suitable include flat rolling in the form of sheet, swaging, grooved rolling, or drawing to produce either round polygon or flat sections, and roll flattening round wire to produce tape.

The history of the material prior to the two steps set forth in the preceding paragraph is determined only by expediency. For example, where the initial body is of such dimensions that cold working to the final configuration is unfeasible, it may involve whatever sequence of hot and cold working steps may usefully be incorporated to yield a configuration of such dimensions as to be amenable to the necessary cold working.

The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 on coordinates of coercivity H in oersteds on the ordinate and annealing temperature in degrees centigrade on the abscissa is a graphical representation showing variations in the coercive force as a function of final heat treatment for materials which have undergone the requisite cold reduction;

FIG. 2 on coordinates of percent change in coercive force on the ordinate and stress in kilograms per square millimeter on the abscissa is a graphical representation showing a comparison of the change of coercive force between a material of the present invention and a conventional twistor material; and

FIG. 3 is a view of a magnetic memory device utilizing an element constructed of a material of this invention.

Detailed description of FIGS. 1 and 2 is in terms of the following examples describing processing conditions which resulted in the material upon which the curves were based.

EXAMPLE I 743.88 grams of cobalt, representing 82 weight percent of the final composition, and 108.86 grams of iron, representing 12 weight, percent of the final composition were placed in an alumina crucible, approximately 4 inches in height having an inner diameter of 2% inches and having a hole in the bottom thereof which was sealed with an alumina stopper rod. 54.43 grams of gold, representing 6 weight percent of the final composition were placed in a separate cup to be added at a later stage in the processing. The alumina crucible was placed in a vacuum induction furnace which was evacuated and pumped down to approximately 10" torr. Next, the cobalt-iron charge was melted at a temperature of approximately 1600" C. Following, the temperature of the system was reduced to approximately l,525 C., the gold added and the temperature increased to approximately l,550 C. and held thereat for 5 minutes. The resultant melt was then bottom poured into a water cooled copper mold to yield an as-cast ingot approximately 16 inches in length by 34 of an inch in diameter,

weighing approximately 2 pounds. The ingot was machined to five-eights of an inch in diameter and heated to a temperature of 925 C. for 2 hours in a hydrogen ambient. Following, the ingot was swaged with reheating between steps, as required, at 925 C. in hydrogen until a diameter of 0.107 inch was attained. At that point, the resultant wire was annealed at 925 C. in hydrogen for 1 hour and then cold-drawn further to various smaller diameters.

A series of wire specimens were prepared in the foregoing manner representing five difierent levels of reduction of area (0 percent, 53 percent, 77 percent, 94.5 percent and 97.5 percent, as defined by the equation wherein t and t, are as previously defined) prior to final aging treatment. The wire representing 0 percent reduction-in-area was given a solution treatment for 2 hours at 1,050 C. which resulted in complete recrystallization of the material. Individual specimens were then cut from each of the wires and given a final 2-hour heat treatment at a temperature within the range of 400l ,000 C.

FIG. 1 is a graphical representation on coordinates of coercive force against final heat treatment temperature for specimens representing each of the levels of cold work. It is to be noted that the specimens which had been solution treated at l,050 C. (0 percent reduction in area) exhibited a small coercive force peak at 775 C., this peak force being less than 3 oersteds. As the amount of prior cold work increases, the peak coercive force increases and the temperature of the peak shifts downwards. This, the specimen having a prior reduction-in-area of 97.5 percent evidenced a peak coercive force of approximately 14.3 oersteds at 500 C. Accordingly, it is evident that cold working prior to the aging treatment greatly enhances the coercive force and lowers the temperature for obtaining maximum coercive force. As is known to those skilled in the art, higher temperatures may be used to accomplish similar results in a shorter period of time.

EXAMPLE n The procedure of Example I was repeated to the annealed 0.107-inch diameter wire stage. The wire was then cold drawn to a diameter of 0.025 inch. At that point the wire was strand annealed in nitrogen at a rate of 24 feet per minute in a furnace having a 6-foot long heat zone. The annealed wire was then further drawn to a diameter of approximately 2 mils and roll flattened to a tape approximately 0.0005 inch thick. The tape was given a final strand anneal for 2 seconds at 850 C. An evaluation of the stress sensitivity of the coercive force of the resultant tape was carried out using a 60 cycle loop tracer and an applied field of 50 oersteds. The values of coercive force with various applied tensile stresses (0') were then determined and plotted in FIG. 2 as percent change in coercive force, [I-Ic(o')Hc(o-0)/Hc(00)]X100 against stress. As noted in FIG. 2, the data reveal a small negative change which is approximately linear with increasing stress. The change in coercive force is 3.3 percent at an applied tension of 4.9 kilograms per square millimeter, indicating a low level of magnetostriction.

For comparative purposes, stress sensitivity measurements were conducted with an alloy of 2.6 percent vanadium containing equal amounts of iron and cobalt, a prior art composition employed in the piggyback twistor. The high stress sensitivity of the coercive force of this alloy can be noted with a change in coercive force of approximately 38 percent at a stress of 2.5 kilograms per square millimeter, such alloy having a high magnetostrictive value.

The device of FIG. 3 is a memory element known as a piggyback twistor. Shown in the H0. is a conductor about which there is disposed a first helical winding 12 of a different magnetic material. The material of winding 12 may be a composition processed in accordance with the invention. For purposes of describing the illustrative memory element shown in FIG. 3, a single information address will be assumed to be defined thereon.

Defining an information address on conductor 10 and its magnetic components 11 and 12, is a coupled winding 13, one end of which, as one end of the conductor 10, is connected to ground. The other ends of the winding 13 and the conductor 10 are connected respectively, to a pair of ganged wipers 14 and 15 of a two-position switch having a pair of w and a pair of r contacts. x and y write current pulse sources 16 and 17 are connected to the w contacts contacted by the wipers l5 and 14 respectively. A read current pulse source 18 is connected to the r contact contacted by the wiper 14 and an information utilization circuit 19 is connected to the r contact contacted by the wiper 15. Common conductor 10 is connected to an input circuit and an output circuit during the respective write and read phases of operation.

The introduction of an information bit in the information address of conductor 10 is accomplished as follows:

With the wipers l5 and 14 in the w position, coincident write currents from the x and y sources 16 and 17, respectively, induce a primary magnetization in the helical component 12 at the information address. The field of the primary magnetization induces a slave magnetization in component 11 which latter magnetization may be sensed by an applied return field. The latter field is generated with the wipers l4 and 15 at the r positions when a read current pulse is applied from source 18. The output signal voltage representative of the stored information value will be generated in common conductor l0 and then transmitted to the utilization circuit 19 via the wiper 15. When the read current pulse is terminated, the field of the primary magnetization again restores the slave magnetization to its normal polarity without the application of accessory circuitry or external power expenditure.

The invention has necessarily been described in terms of limited number of exemplary embodiments. While these are considered adequate to illustrate the advantageous use of any of the materials herein in an electrically alterable permanent memory device, they are not to be construed as limiting.

What we claim is:

1. A device including a ferromagnetic body comprising an alloy consisting essentially of 75-95 weight percent cobalt, 0.5-]? weight percent gold, remainder iron produced by cold working so as to result in a thickness reduction of at least 20 percent as determined from r,z,/r, in which t, and are a dimension ofa body subject to reduction by working, the said body having associated therewith at least one electrical conducting path so situated that passage of current throughout said path results in a magnetic flux within at least a portion of the said body.

2. A device in accordance with claim 1 in which the said electrical current path consists of at least one turn of conductive wire about the said body.

3. Device in accordance with claim 1 wherein said alloy is partially annealed at a temperature within the range of 1,000 C.

4. A device comprising a body of material defining at least one magnetically remanent flux path, the said body comprising an alloy consisting essentially of 7595 weight percent cobalt 0.5 l 7 weight percent gold, remainder iron, produced by cold working to result in a thickness reduction of at least 20 percent as determined from the fraction t i /r wherein t, and t are a dimension subject to reduction by working followed by annealing at a temperature in the range of l00l,000 C. for a period of at least 1 second, such body havin associated therewith at least two electrical paths.

5. ev1ce comprising a first magnetic material and a second magnetic material wherein said second magnetic material has a remanent magnetization at least equal to the saturation magnetization of said first magnetic material and a coercivity greater than that of said first magnetic material, the said first and second magnetic materials being magnetically coupled to each other, said second magnetic material consisting essentially of 75-95 weight percent cobalt, 0.5- 1 7 weight percent gold, remainder iron. 

2. A device in accordance with claim 1 in which the said electrical current path consists of at least one turn of conductive wire about the said body.
 3. Device in accordance with claim 1 wherein said alloy is partially annealed at a temperature within the range of 100*-1, 000* C.
 4. A device comprising a body of material defining at least one magnetically remanent flux path, the said body comprising an alloy consisting essentially of 75-95 weight percent cobalt 0.5-17 weight percent gold, remainder iron, produced by cold working to result in a thickness reduction of at least 20 percent as determined from the fraction t1-t2/t1 wherein t1 and t2 are a dimension subject to reduction by working followed by annealing at a temperature in the range of 100-1,000* C. for a period of at least 1 second, such body having associated therewith at least two electrical paths.
 5. Device comprising a first magnetic material and a second magnetic material wherein said second magnetic material has a remanent magnetization at least equal to the saturation magnetization of said first magnetic material and a coercivity greater than that of said first magnetic material, the said first and second magnetic materials being magnetically coupled to each other, said second magnetic material consisting essentially of 75-95 weight percent cobalt, 0.5-17 weight percent gold, remainder iron. 